The present invention relates to the cellular communication arts. It finds particular application in conjunction with a wireless device cradle with spatial antenna diversity capability.
A cellular communication system is a type radio communication system in which communication (i.e. voice and/or data) is permitted with a radio transceiver positioned at any location within a geographic area encompassed by the cellular communication system. A cellular communication system is created by positioning a plurality of fixed-site radio transceivers, referred to as base stations or base sites, at spaced-apart locations throughout a geographic area. The base stations are connected to a conventional, wireline telephonic network such as a Public Switched Telephone Network (PSTN). Associated with each base station of the plurality of base stations is a portion of the geographic area encompassed by the cellular communication system. Such portions are referred to as cells. Each of the plurality of cells is defined by one of the base stations of the plurality of base stations, and the plurality of cells together define the coverage area of the cellular communication system.
A radio transceiver, referred to in a cellular communication system as a cellular radiotelephone or, more simply, a cellular phone, positioned at any location within the coverage area of the cellular communication system, is able to communicate (i.e. voice and/or data) with a user of the conventional, wireline, telephonic network by way of a base station. Modulated carrier signals generated by the radiotelephone are transmitted to a base station, and modulated carrier signals generated by the base station are transmitted to the radiotelephone, thereby to effectuate two-way communication. A signal received by a base station is then transmitted to a desired location of a conventional, wireline network by conventional telephony techniques. Signals generated at a location of the wireline network are transmitted to a base station by conventional telephony techniques, and the base station then transmits the signals to the remote radiotelephone.
In a digital cellular system, a transmitter, converts the communication signal into a digital code that is modulated and then transmitted upon the communication channel. Ideally a signal received by the receiver of a radiotelephone is identical with that of the signal transmitted by the transmitter of the base station. However, the signal actually received by the receiver is not a single signal but rather the summation of signals that have propagated along different paths.
For example, a signal transmitted by the transmitter may be reflected off of both man-made or natural objects prior to reception by the receiver, and signals transmitted upon such paths are received by the receiver, delayed in time relative to signals transmitted upon the shortest-distance paths. This multiplicity of transmission paths is referred to as a multipath signals, and the signal received by the receiver is a summation of the plurality of the multipath signals.
Because signals transmitted along other than the shortest-distance transmission paths arrive at the receiver delayed in time relative to the signal transmitted along the shortest-distance transmission path, late-arriving signals interfere with previously arrived signals. When the signal transmitted by the transmitter comprises the modulated, digital code, such interference is referred to as intersymbol interference. When such intersymbol interference is significant, a received signal cannot be faithfully recovered by a remote receiver.
Receivers have been constructed which have two or more spaced-apart antennas for receiving signals transmitted thereto. It is known that the larger the spacing between antennas, the more decorrelated are the received signals. When two or more antennas are configured in such manner, the antennas are referred to as being in diversity (or, diversity antennas), and a receiver including such antennas configured in diversity are referred to as diversity receivers. Transceivers including such antennas are referred to as diversity transceivers.
The signals received at one or the other of the two or more spaced-apart antennas are utilized by circuitry of the receiver to recover the signal actually transmitted by the transmitter. The antennas are positioned in relative orientations such that when a signal received at one of the antennas includes significant interference or is weak, a signal received at another of the antennas includes, typically, a lesser amount of interference (or may be of a greater signal strength). This is because of the different propagation paths signals travel in reaching the two antennas.
Although the path from a transmitter to one of the two remote antennas may cause signal phase cancellation that results from different signal paths, it is less probable that multiple paths to the other antenna will cause phase cancellation at the same time. The probability that the two antennas are receiving exactly the same signal is called a correlation factor.
Wireless subscriber devices have inherent limitations due to their small size. The radio performance tends to be poor because their small size hinders the use of such spatial antenna diversity techniquesxe2x80x94both from the aspect of having the size to provide the electronics for the multiple receiver paths, and providing enough physical separation of the multiple antennas to achieve any improvement. There is also an issue of increased cost. These limitations contribute to not being able to provide very high data rates that are demanded by future 3G (third generation) services and applications. It also prevents the cellular network operator from meeting range and capacity expectations of the deployed system.
Accordingly, it is desirable to develop a new and improved wireless device with spatial reception and/or transmit antenna diversity capability.